f the sixteenth century. In an edition of
Vegetius on the _Art of War_, published in 1511, there is an engraving
of a diver walking in the sea with a cap over his head and shoulders,
from which a flexible tube rises to the surface. This was, no doubt,
the embryo of our "diving-dress." John Taisner, in 1538, says that he
saw two Greeks, at Toledo in Spain, make experiments with diving
apparatus, in presence of the Emperor Charles the Fifth and ten thousand
spectators. Gaspar Schott of Numberg, in 1664, refers to this Greek
machine as an "aquatic kettle;" but mentions, as preferable in his
estimation, a species of "aquatic armour," which enabled those who wore
it to walk under water. The "aquatic kettle" was doubtless the embryo
of the diving-bell.

From that time onward inventive minds have been turned, with more or
less success, towards the subject of submarine operations, and many are
the contrivances--clever, queer, absurd, and useful--which have been the
outcome. Not content with "kettles" and "bells," by means of which they
could descend into the deep and remain there for an hour or more at a
time, and with "armour" and "dresses" with which they could walk about
at the bottom of the sea, men have constructed several submarine boats
and machines, in which, shut up like Jonah in the whale, they purposed
to move about from place to place, sink to the bottom and rise to the
surface, at will, or go under the bottoms of enemy's ships and fix
torpedoes wherewith to blow them up, and otherwise do them damage.
These latter machines have not attained to any noteworthy degree of
success--at least they have not yet done either much good or much harm
to the human race; but the former--the "kettles" and the "armour,"--in
other words, the "diving-bells" and "dresses"--have attained to a high
degree of perfection and efficiency, and have done incalculable good
service.

The diving-bell was so styled owing to the first machines being made in
the shape of a gigantic bell. An inverted wine-glass, thrust mouth
downwards into water, will not fill with water, owing to the air which
it contains keeping the water out. It will partially fill, however,
because air is compressible, and the deeper down it is thrust the more
will the air be compressed. At a depth of thirty-three feet the air
will be compressed to half its bulk--in other words, the glass will be
half-full of water. It is clear that a fly or any small insect could
liv